Field of the Invention
The invention relates to an exhaust gas catalytic converter, particularly for an internal combustion engine, including a carrier body being formed of sheet-metal layers and having a structure through which exhaust gas can flow for receiving a catalytic coating, the carrier body being disposed in a flow channel carrying the exhaust gas and being externally heatable. The invention also relates to a method for producing the exhaust gas catalytic converter.
In such catalytic converters as well, improved efficiency in catalytic reburning of exhaust gases prevails at higher operating temperatures. In order to attain improved conversion performance, particularly in the cold-starting phase, while the catalytic converter is still at low operating temperatures, it is known to heat the metal carrier body electrically. The electrical power supply of the vehicle is used as the current source therefor. The electrical heating can be turned off once the catalytic converter, or the carrier body provided with the catalytic coating, has reached its operating temperature because of the flow of the hot exhaust gas through it.
In a catalytic converter of that generic type, which is known from Published International Application WO 89/10471, an electrically conductive carrier body is provided, which includes wound, stacked or otherwise stratified corrosion-proof metal sheet-metal layers. The sheet-metal layers are disposed in such a way as to lend the carrier body a structure, for a catalytic coating, that exhaust gas can flow through. That is attained in particular by layering smooth sheet-metal layers and corrugated sheet-metal layers alternatingly on one another. That kind of carrier body, which may have various cross-sectional shapes, is then received in a flow channel or jacket housing that carries the exhaust gas flow. In order to heat the carrier body, it is connected to a voltage source, in particular the power supply of the motor vehicle. The electrical resistance of the carrier body serves to heat it. The carrier body has gaps and/or electrically insulating intermediate layers to achieve an electrical separation.
In a catalytic converter known from U.S. Pat. No. 3,770,389, a carrier body of ceramic material for a catalytic coating is provided that has the shape of a hollow cylindrical structure with an annular cross-sectional area. In a central hollow space of the carrier body, which has a flow passing through it axially, there is a carrier body including sheet-metal layers and having a catalytic coating. That body substantially includes an axially disposed metal bar which is spirally wound about by a steel band. If that kind of metal carrier body is connected to a voltage source, its electrical resistance causes heating. In the starting phase, that results in improved efficiency and leads to heating of the monolithic carrier body. Once the latter has reached its operating temperature, the metal carrier body is disconnected from the voltage source.
Another model is known from German Published, Prosecuted Application DE-AS 22 30 663. In that case, a ceramic carrier body which is constructed as a hollow cylinder is heated by a centrally disposed electrical heating element. The heating element, which is constructed to be self-insulating, has a heating coil that is disposed in a metal cylinder and is connected to a power supply.
Published European Application No. 0 233 860 A3 discloses an apparatus for cleaning combustion exhaust gases of an internal combustion engine, in particular a Diesel engine. That apparatus has a retaining or filter device in which finely divided condensates or particles such as soot can be retained. The filter body of the particle retaining or filter device, for instance, includes a wound steel nonwoven material with catalyst-coated metal elements having interstices or a catalyst-coated honeycomb filter. For instance, if after relatively long operation of the engine, soot sticks firmly in the filter device, the layer must be removed from the catalytic surface. That is done by the burn-off initiating device (heating cartridge), having a surface which is likewise provided with a catalytic lining and having a surface which rests directly on the filter body. By electrically heating the heating cartridge, burn-off of the soot layer on its surface and therefore in the filter body is initiated, since the burnoff front created at the heating cartridge jumps over to the filter body, where it propagates through the filter body.
U.S. Pat. No. 3,889,464 describes an embodiment of a catalytic converter having channels, that are catalytically coated on their inner surface, which form a honeycomb structure, and in which wires are pulled along the centers of the channels, with the wires being electrically connected into empty space and connected between the terminals, each at the end surfaces of the honeycomb body. That causes indirect heating of the catalytic surface of the honeycomb body. In another embodiment, the catalytic converter is formed essentially by likewise heatable heating elements extending in a hollow chamber along the flow direction of the fluid. They are likewise catalytically coated on their surface and therefore lead to direct heating of the catalytic converter.